1. Field of the Invention
The present invention relates to a light-emitting device in which light extraction efficiency is improved and a method for manufacturing the same.
2. Description of the Related Art
Recently, a semiconductor light-emitting device, especially a light-emitting diode (LED), is widely used in a backlight for a display, an in-vehicle device, an illumination device, and the like. A semiconductor light-emitting device having high luminous efficiency is demanded in such applications. The improvement of the light extraction efficiency of the device is one of promising measures for enhancing the luminous efficiency of the semiconductor light-emitting device. Therefore, research is being conducted on the improvement of light extraction efficiency.
For example, in the light-emitting device in which a substrate having a high refractive index is used, a light is reflected on a substrate surface and at an interface due to a large difference in refractive index with the outside, and some light component cannot be extracted to the outside because an output angle is not lower than the critical angle of total reflection. They cause a problem of a light extraction loss.
In a method of preventing the light extraction loss, there is known a technique of forming a high-refractive-index resin layer on the substrate surface or of performing a nanometer-scale irregularity surface treatment in order to obtain an anti-reflection effect or a diffraction effect.
However, in the conventional nanometer-scale irregularity surface treatment which is considered to efficiently extract the light emitted inside the light-emitting device to the outside (for example, see JP-A 2003-258296 and 2007-184313), since a complicated process such as etching is required to actually form the roughed surface, a theoretical optimum shape is hardly formed at an optimum position.